tree b6055dce972162efde4d3d2748ca7096ee1d68d4
parent 0726681a7080cef6a9fd414894690fac16418772
author Ian Armstrong <ian@iarmst.demon.co.uk> 1261447166 -0300
committer Mauro Carvalho Chehab <mchehab@redhat.com> 1267207841 -0300

V4L/DVB: ivtv: Fix race condition for queued udma transfers

There are several DMA related interrupts which wake up the dma_waitq. The udma
routines use this queue while they wait for their transfer to complete. When
woken, the udma routine will check the IVTV_F_I_UDMA_PENDING & IVTV_F_I_UDMA
flags to see if the transfer is still queued or has finished. However, a small
window exists between the IVTV_F_I_UDMA_PENDING flag being cleared and the
IVTV_F_I_UDMA flag being set. Given that the completion of an unrelated DMA
transfer may wake up the udma routine, it's possible for this check to fail
and the udma routine will start unmapping pages when the transfer has only
just started. The result of this is unpredictable.

This fix simply delays the clearing of the IVTV_F_I_UDMA_PENDING flag until
after IVTV_F_I_UDMA has been set.

Signed-off-by: Ian Armstrong <ian@iarmst.demon.co.uk>
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>